Decoding Myofascial Pain: Windup Phenomenon as A Key Diagnostic Measure

Myofascial pain syndrome (MPS) is a common musculoskeletal pain disorder with increased prevalence in individuals with comorbidities including cancer, stroke, osteoarthritis, mental health conditions, and more. Despite its prevalence, there is a lack of clinically feasible, evidence-based outcome measures for MPS diagnosis. The windup phenomenon is a frequency-dependent increase in neuronal excitability to input stimuli, facilitating temporal summation of pain that's commonly associated with central sensitization. Emerging evidence strongly links myofascial pain pathophysiology to central sensitization. This study aims to investigate the physiologic expression of the windup phenomenon in different MPS clinical phenotypes to assess its clinical feasibility as a psychophysical diagnostic outcome measure. A cross-sectional analysis categorized myofascial pain patients into three groups: active (n=12) with spontaneous pain, latent (n=6) with pain upon palpation but not spontaneously, and pain-free controls (n=6). An experienced physiatrist or physical therapist determined group classification. The windup phenomenon was bilaterally tested over the trapezius muscle using a 16-pinprick stimulus at 1 Hz with a 256 mN weighted pinprick (MRC Systems, Heidelberg, Germany). The Sumsquare outcome measure (Clouse, 2021) quantified windup magnitude. Significant increases in Sumsquare were observed in the active group compared with latent (374, 95%CI [36.6,711], p=0.0287) and controls (377, 95%CI [47.9,707], p=0.0242). No Sumsquare difference was observed between latent and normal groups (3.54, 95%CI [-122,130], p=0.9997). Symptomatic myofascial pain patients exhibit enhanced windup compared to asymptomatic latent and control groups, suggesting windup's clinical feasibility as a psychophysical outcome measure in myofascial pain phenotyping. Larger studies are needed for further validation.